
/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 *版权所有2002-2016原作者。
 *
 *根据Apache许可证2.0版（“许可证”）许可；
 *除非符合许可证的规定，否则您不得使用此文件。
 *您可以在以下网址获取许可证副本
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 *除非适用法律要求或书面同意，否则软件
 *根据许可证分发是在“按原样”的基础上分发的，
 *无任何明示或暗示的保证或条件。
 *有关管理权限的特定语言，请参阅许可证
 *许可证下的限制。
 */

package org.springframework.context.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Indicates that a bean should be given preference when multiple candidates
 * are qualified to autowire a single-valued dependency. If exactly one
 * 'primary' bean exists among the candidates, it will be the autowired value.
 *
 * <p>This annotation is semantically equivalent to the {@code <bean>} element's
 * {@code primary} attribute in Spring XML.
 *
 * <p>May be used on any class directly or indirectly annotated with
 * {@code @Component} or on methods annotated with @{@link Bean}.
 *
 * <h2>Example</h2>
 * <pre class="code">
 * &#064;Component
 * public class FooService {
 *
 *     private FooRepository fooRepository;
 *
 *     &#064;Autowired
 *     public FooService(FooRepository fooRepository) {
 *         this.fooRepository = fooRepository;
 *     }
 * }
 *
 * &#064;Component
 * public class JdbcFooRepository extends FooRepository {
 *
 *     public JdbcFooRepository(DataSource dataSource) {
 *         // ...
 *     }
 * }
 *
 * &#064;Primary
 * &#064;Component
 * public class HibernateFooRepository extends FooRepository {
 *
 *     public HibernateFooRepository(SessionFactory sessionFactory) {
 *         // ...
 *     }
 * }
 * </pre>
 *
 * <p>Because {@code HibernateFooRepository} is marked with {@code @Primary},
 * it will be injected preferentially over the jdbc-based variant assuming both
 * are present as beans within the same Spring application context, which is
 * often the case when component-scanning is applied liberally.
 *
 * <p>Note that using {@code @Primary} at the class level has no effect unless
 * component-scanning is being used. If a {@code @Primary}-annotated class is
 * declared via XML, {@code @Primary} annotation metadata is ignored, and
 * {@code <bean primary="true|false"/>} is respected instead.
 *
 * @author Chris Beams
 * @author Juergen Hoeller
 * @since 3.0
 * @see Lazy
 * @see Bean
 * @see ComponentScan
 * @see org.springframework.stereotype.Component
 */
/**
 *指示当有多个候选者时，应优先考虑一个bean
 *有资格自动连接单值依赖项。如果正好一个
 *候选中存在“primary”bean，它将是自动连接的值。
 *
 *＜p＞这个注释在语义上等同于{@code＜bean＞}元素的
 *｛@code primary｝属性。
 *
 *<p>可以直接或间接注释在任何类上
 *｛@code@Component｝或在用@｛@linkBean｝注释的方法上。
 *
 *<h2>示例</h2>
 *<pre-class=“code”>
 * &#064;组成部分
 *公共类FooService{
 *
 *私有FooRepository FooRepository；
 *
 *     &#064;自动装配
 *公共FooService（FooRepository FooRepository）{
 *this.fooRepository=fooRepository；
 *     }
 * }
 *
 * &#064;组成部分
 *公共类JdbcFooRepository扩展FooRepository{
 *
 *公共JdbcFooRepository（数据源DataSource）{
 *         // ...
 *     }
 * }
 *
 * &#064;主要的，重要的
 * &#064;组成部分
 *公共类Hibernate FooRepository扩展FooRepository{
 *
 *公共Hibernate FooRepository（会话工厂会话工厂）{
 *         // ...
 *     }
 * }
 *</pre>
 *
 *<p>因为{@code HibernateFooRepository}被标记为{@code@Primary}，
 *它将优先注入，而不是基于jdbc的变体，假设两者
 *在同一个Spring应用程序上下文中作为bean存在
 *通常是自由应用组件扫描的情况。
 *
 *<p>请注意，在类级别使用{@code@Primary}没有任何效果，除非
 *正在使用组件扫描。如果一个｛@code@Primary｝注释的类是
 *通过XML声明，｛@code@Primary｝注释元数据被忽略，并且
 *{@code<bean-primary=“true|false”/>}得到尊重。
 *
 *@作者Chris Beams
 *@作者Juergen Hoeller
 *@自3.0起
 *@见懒惰
 *@见憨豆
 *@请参阅组件扫描
 *@参见org.springframework.stereotype.Component
 */
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Primary {

}
